ImportC: improve error message for size_t (#21187)

Resolves: https://github.com/dlang/dmd/issues/20414

Add some hints for common missing includes.

compiler/src/dmd/expressionsem.d

@@ -4116,16 +4116,28 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
 
         /* Look for what user might have meant
          */
-        if (const n = importHint(exp.ident.toString()))
+        if (!(sc && sc.inCfile))
-            error(exp.loc, "`%s` is not defined, perhaps `import %.*s;` is needed?", exp.ident.toChars(), cast(int)n.length, n.ptr);
+        {
-        else if (auto s2 = sc.search_correct(exp.ident))
+            if (const n = importHint(exp.ident.toString()))
-            error(exp.loc, "undefined identifier `%s`, did you mean %s `%s`?", exp.ident.toChars(), s2.kind(), s2.toChars());
+                error(exp.loc, "`%s` is not defined, perhaps `import %.*s;` is needed?", exp.ident.toChars(), cast(int)n.length, n.ptr);
-        else if (const p = Scope.search_correct_C(exp.ident))
+            else if (auto s2 = sc.search_correct(exp.ident))
-            error(exp.loc, "undefined identifier `%s`, did you mean `%s`?", exp.ident.toChars(), p);
+                error(exp.loc, "undefined identifier `%s`, did you mean %s `%s`?", exp.ident.toChars(), s2.kind(), s2.toChars());
-        else if (exp.ident == Id.dollar)
+            else if (const p = Scope.search_correct_C(exp.ident))
-            error(exp.loc, "undefined identifier `$`");
+                error(exp.loc, "undefined identifier `%s`, did you mean `%s`?", exp.ident.toChars(), p);
+            else if (exp.ident == Id.dollar)
+                error(exp.loc, "undefined identifier `$`");
+            else
+                error(exp.loc, "undefined identifier `%s`", exp.ident.toChars());
+        }
         else
-            error(exp.loc, "undefined identifier `%s`", exp.ident.toChars());
+        {
+            if (const n = cIncludeHint(exp.ident.toString()))
+                error(exp.loc, "`%s` is not defined, perhaps `#include %.*s` is needed?", exp.ident.toChars(), cast(int)n.length, n.ptr);
+            else if (auto s2 = sc.search_correct(exp.ident))
+                error(exp.loc, "undefined identifier `%s`, did you mean %s `%s`?", exp.ident.toChars(), s2.kind(), s2.toChars());
+            else
+                error(exp.loc, "undefined identifier `%s`", exp.ident.toChars());
+        }
 
         result = ErrorExp.get();
     }

compiler/src/dmd/imphint.d

@@ -26,8 +26,15 @@ const(char)[] importHint(const(char)[] s) @safe
         return *entry;
     return null;
 }
+const(char)[] cIncludeHint(const(char)[] s) @safe
+{
+    if (auto entry = s in cHints)
+        return *entry;
+    return null;
+}
 
 private immutable string[string] hints;
+private immutable string[string] cHints;
 
 shared static this()
 {
@@ -83,6 +90,23 @@ shared static this()
         "InterpolationHeader": "core.interpolation",
         "InterpolationFooter": "core.interpolation",
     ];
+    cHints = [
+        "NULL": "<stddef.h>",
+        "calloc": "<stdlib.h>",
+        "fopen": "<stdio.h>",
+        "fprintf": "<stdio.h>",
+        "free": "<stdlib.h>",
+        "malloc": "<stdlib.h>",
+        "memcpy": "<string.h>",
+        "memmove": "<string.h>",
+        "memset": "<string.h>",
+        "printf": "<stdio.h>",
+        "ptrdiff_t": "<stddef.h>",
+        "size_t": "<stddef.h>",
+        "stderr": "<stdio.h>",
+        "stdin": "<stdio.h>",
+        "stdout": "<stdio.h>",
+    ];
 }
 
 unittest

compiler/src/dmd/typesem.d

@@ -169,17 +169,28 @@ private void resolveHelper(TypeQualified mt, Loc loc, Scope* sc, Dsymbol s, Dsym
          */
         const p = mt.mutableOf().unSharedOf().toChars();
         auto id = Identifier.idPool(p[0 .. strlen(p)]);
-        if (const n = importHint(id.toString()))
+        if (!(sc && sc.inCfile))
-            error(loc, "`%s` is not defined, perhaps `import %.*s;` ?", p, cast(int)n.length, n.ptr);
+        {
-        else if (auto s2 = sc.search_correct(id))
+            if (const n = importHint(id.toString()))
-            error(loc, "undefined identifier `%s`, did you mean %s `%s`?", p, s2.kind(), s2.toChars());
+                error(loc, "`%s` is not defined, perhaps `import %.*s;` ?", p, cast(int)n.length, n.ptr);
-        else if (const q = Scope.search_correct_C(id))
+            else if (auto s2 = sc.search_correct(id))
-            error(loc, "undefined identifier `%s`, did you mean `%s`?", p, q);
+                error(loc, "undefined identifier `%s`, did you mean %s `%s`?", p, s2.kind(), s2.toChars());
-        else if ((id == Id.This   && sc.getStructClassScope()) ||
+            else if (const q = Scope.search_correct_C(id))
-                 (id == Id._super && sc.getClassScope()))
+                error(loc, "undefined identifier `%s`, did you mean `%s`?", p, q);
-            error(loc, "undefined identifier `%s`, did you mean `typeof(%s)`?", p, p);
+            else if ((id == Id.This   && sc.getStructClassScope()) ||
-        else
+                     (id == Id._super && sc.getClassScope()))
-            error(loc, "undefined identifier `%s`", p);
+                error(loc, "undefined identifier `%s`, did you mean `typeof(%s)`?", p, p);
+            else
+                error(loc, "undefined identifier `%s`", p);
+        }
+        else {
+            if (const n = cIncludeHint(id.toString()))
+                error(loc, "`%s` is not defined, perhaps `#include %.*s` ?", p, cast(int)n.length, n.ptr);
+            else if (auto s2 = sc.search_correct(id))
+                error(loc, "undefined identifier `%s`, did you mean %s `%s`?", p, s2.kind(), s2.toChars());
+            else
+                error(loc, "undefined identifier `%s`", p);
+        }
 
         pt = Type.terror;
         return;

compiler/test/fail_compilation/test20414.c

@@ -0,0 +1,15 @@
+/* TEST_OUTPUT:
+---
+fail_compilation/test20414.c(1): Error: `size_t` is not defined, perhaps `#include <stddef.h>` ?
+fail_compilation/test20414.c(2): Error: `ptrdiff_t` is not defined, perhaps `#include <stddef.h>` ?
+fail_compilation/test20414.c(3): Error: `NULL` is not defined, perhaps `#include <stddef.h>` is needed?
+fail_compilation/test20414.c(5): Error: undefined identifier `fooo`, did you mean function `foo`?
+---
+*/
+
+#line 1
+size_t x;
+ptrdiff_t pd;
+void *p = NULL;
+void foo(void);
+void (*fp)(void) = &fooo;

compiler/test/fail_compilation/test23003.c

@@ -1,6 +1,6 @@
 /* TEST_OUTPUT:
 ---
-fail_compilation/test23003.c(101): Error: undefined identifier `size_t`
+fail_compilation/test23003.c(101): Error: `size_t` is not defined, perhaps `#include <stddef.h>` ?
 fail_compilation/test23003.c(102): Error: undefined identifier `object`
 ---
 */